1. Field of the Invention
This invention relates to liquid chemical feeding systems and more particularly to a improved vacuum feeding system for feeding liquid chemicals at a controlled uniform rate into a pressurized stream of another liquid flowing in a conduit, or into another liquid in a storage container at atmospheric pressure.
2. Description of the Prior Art
Vacuum feed systems employing a venturi to produce the vacuum for introducing liquid chemicals into other liquids are well known. Such systems are commonly employed in water and sewage treatment facilities for injecting liquid treatment chemicals into pressurized pipes, storage tanks or pools. For example, systems are known for feeding sodium hypochlorite solution (hereinafter sometimes called liquid chlorine) into water treatment systems using a venturi to induce the liquid chlorine flow and employing a flow meter with a flow rate adjusting valve. The use of vacuum regulators and differential pressure regulators in such systems is known.
Despite the attempts to control flow, all the known systems have had difficulty in maintaining a continuous set feed rate, which may be critical, for example when dispensing liquid chlorine into drinking water at the precise rates required by regulating agencies. Also, such known systems frequently cannot repeat a set feed rate in start and stop operation.
Another problem encountered in the known systems when used to feed liquid chlorine is the propensity of this chemical to “off gas” air and chlorine gas which can form bubbles in the system and interfere with its smooth operation.
U.S. Patent 2002/017083 to Alexander disclosures one known vacuum system for the addition of a chemical into water either in a swimming pool or into potable water. The chemical used in this invention is liquid chlorine such as sodium hypochlorite. A venturi is connected into the water feed line, and an additive stream inlet is connected to the venturi. A metering valve is used to set the flow rate of the chemical being added, and a flow meter provides a visual indication of the flow rate of the chlorine additive. The chlorine being added is fed via input line into a U-shaped feed line which includes a solenoid operated valve (25) connected to a microprocessor (26) which senses when additional chlorine needs to be added to the water. A shut off valve and a clean out valve permits cleaning the U-shaped feed line. All the components of the feed line are constructed of corrosive resistant material as are the piping and joints which connect the components together.
The liquid feed system disclosed in the Alexander patent does not contain means for positively preventing back-flow of liquid through the system, and its construction is such as to make it particularly susceptible to trapping gas bubbles.
U.S. Pat. Nos. 5,827,959; 5,285,808; 3,194,254; and 3,187,764 disclose systems for feeding gaseous chemicals into a liquid, using a venturi to apply a suction to the gaseous chemical feed line. The feeding of a liquid into another liquid at a controlled rate presents problems well-known to those skilled in the art, which problems are not found in feeding a gas into a liquid.